Guys, I've heard that you can pull a 5.7 and replace it with a 4.3 with min issues to motor mounts and exhuast issue's, does anyone have experience with this or the other way around...I know most people won't understand why but its just weight and preference.....

The 4.3 is basiclly a 5.7 less 2 cylinders. Everything else is the same. Will bolt right up to you trans.

John is correct, the nice thing about them also is when you rebuild them you can use 350 parts and save yourself some cash, the rods rings and pistons are the same also.... Their is a guy here locally who races dirttrack with a 4.3 and smokes the V8's all the time...

Good Luck

Actually I'm more concerned about the accessories, mounting points, and more-over the loss in hp/torque but this could be made up as I hear people get 220 hp and around 200 lb/ft of torque....this is more then my 350 but I guess I need to go Caprice shopping and bring a tape measure to see what can be done.....

All engine accessories should be a direct bolt on. If you are using a carb, not FI, there really shouldn't be any issues. Water pump concerns if your running serp belt vs v-belts. all mounting holes are in the same place. If you go FI. try to find a Vortec engine...245hp..not sure of torque? Good Luck
S-10 worked for me...installed in a 67 Mercedes 300...used engine, trans and d-shaft...all S-10 brackets for p/s, alt, a/c..didn't use smog pump.
Ps...you can even move engine assembly forward for more rear shaft length if needed...will need to move mounts though.